Vinyl chloride and vinylidene chloride polymers are known to be self-extinguishing and relatively more flame retardant than other polymers such as polyethylene, polypropylene and the like. However, a substantial amount of smoke may be produced upon exposure of vinyl chloride and vinylidene chloride polymers to a flame. Conventional flame retardants such as antimony oxide do not aid in smoke reduction.
The following art is related to the present invention. Salts and oxides of nickel or zinc are effective in amounts up to several percent as condensing agents for polyvinyl halides (U.S. Pat. No. 2,157,997). ZnSO.sub.4 can be used together with an alkanolamine to improve heat degradation resistance of vinyl halide resins (U.S. Pat. No. 3,652,619). Alkali metal zinc ferrocyanides can be compounded with vinyl chloride polymers to produce improved flame resistance and to reduce smoke production (U.S. Pat. No. 3,822,234). Ger. Pat. No. 2,330,022 teaches preparation of filled thermoplastic polymer compositions such as PVC containing a carbonate such as ZnCO.sub.3. Anticorrosive vinyl chloride resins are obtained by compounding the resins with ZnO, ZnCO.sub.3, or certain other metallic compounds (Japan Ser. No. 73-37,742). The stabilizing effect of ZnSO.sub.4, zinc oxide and other compounds on unplasticized polyvinyl chloride was evaluated in 6 Kunstoffe-Plastics 165-168(1959) (53 Chem.Abs.23049f). The fact that an additive is a flame retardant does not necessarily mean that it will have good smoke retardant properties, as is well known to those skilled in the art. New smoke retardant vinyl chloride and vinylidene chloride polymer compositions are desired.